The present invention relates to a clean molded article which has an excellent plasma resistance and an excellent property of inhibiting elution of metals, has a reduced content of impurity metals and can give a sealing member to be used for sealing of a semiconductor manufacturing equipment.
In manufacturing semiconductor elements, very high cleanliness is required, and the requirements for high cleanliness range over not only management of a production process of semiconductors but also a semiconductor manufacturing equipment itself and parts of such equipment. Even if the parts of semiconductor manufacturing equipment are cleaned after built in the equipment, a degree of possible cleanliness is limited. Such parts are required to have been cleaned highly before built in the equipment. Contamination which becomes a problem particularly in the production of semiconductors is caused by fine particles, organic compounds and elution of metals which have an adverse effect on accurate etching treatment.
Also high cleanliness is required similarly in a molded article such as a sealing member for semiconductor manufacturing equipment which the present invention can be particularly suitably applied to. The present applicants have attained high cleanliness of the sealing member itself by employing a special method of cleaning the sealing member after molding (WO99/49997).
Such a sealing member is produced by crosslinking a crosslinkable elastomer composition such as a rubber, and in order to provide the sealing member with mechanical properties, there is a case where a carbon black is added as a filler to the composition.
In production of semiconductors, there is a case where a dry process such as plasma etching is carried out. In that dry process, there is a case where particles (impurity fine particles) are generated from molded parts produced from an elastomer. Those contaminating sources must be eliminated.
Also with respect to the sealing member used in a wet process such as cleaning process, it is desired to reduce elution of metals more.
The present invention relates to a molded article which has an excellent plasma resistance and an excellent property of metal-elution inhibition and can be obtained by crosslinking a crosslinkable elastomer composition containing a carbon black which has a reduced content of impurity metals and causes no crosslinking failure even if not only radiation crosslinking but also crosslinking with a peroxide crosslinking agent is carried out.
Namely the present invention relates to an elastomer molded article which is obtained by crosslinking a crosslinkable elastomer composition comprising a crosslinkable elastomer component and a carbon black filler having an average particle size of not more than 700 xcexcm and an impurity metal content measured by an ashing analysis method of not more than 300 ppm. The elastomer molded article has an impurity metal content measured by an ashing analysis method of not more than 100 ppm and (1) an increasing rate of particles generated by irradiating oxygen plasma to the article is not more than 500% or (2) an amount of impurity metals extracted from the article with a 50% aqueous solution of HF is not more than 500 ppb.
In case where the molded article is used in a dry process, it is particularly preferable to use a graphitized carbon black filler. It is desirable that an average particle size of such a graphitized carbon black filler is from 10 to 100 xcexcm, preferably from 10 to 30 xcexcm from the viewpoint of inhibiting generation of particles after plasma irradiation.
The graphitized carbon black filler having a reduced content of impurity metals can be obtained by heat-treating a starting carbon black filler at high temperature.
When a carbon black filler containing a very small amount of impurity metals is used, the obtained molded article is particularly excellent in property of metal-elution inhibition and is used suitably for wet process. In that case, there is no problem even if an average particle size is relatively large.
According to the present invention, the crosslinkable elastomer composition obtained by adding the above-mentioned specific carbon black filler to a fluorine-containing elastomer component or a silicone elastomer component can give a sealing member having excellent mechanical and chemical properties. Further the sealing member is treated by a special cleaning process disclosed in the above-mentioned WO99/49997, namely a process for cleaning with ultrapure water, a process for cleaning with a clean organic compound in the form of liquid at a cleaning temperature or with a clean inorganic aqueous solution, a dry etching cleaning process or an extractive cleaning process, and thus a molded article for semiconductor manufacturing equipment which has a very high cleanliness and has an excellent plasma resistance and an excellent property of metal-elution inhibition can be obtained.
The carbon black filler to be used in the present invention is a carbon black filler having an impurity metal content measured by an ashing analysis method of not more than 300 ppm and an average particle size of not more than 700 xcexcm.
As the carbon black filler, there are a graphitized carbon black filler having a relatively small particle size and suitable for a dry process requiring plasma resistance and a carbon black filler having a low content of impurity metals (not more than 100 ppm) and suitable for a wet process requiring metal-elution inhibition property.
Among them, examples of the graphitized carbon black are, for instance, TOCABLACK #3885, #3855, #3845 and #3800 available from Tokai Carbon Kabushiki Kaisha, and the like. Particularly preferred is a carbon black having a specific surface area of not less than 3 m2/g and DBP oil absorption of not less than 15 ml/100 g from the viewpoint of processability.
The graphitized carbon black to be used in the present invention is one having a relatively small average particle size, preferably from 10 to 100 xcexcm, further preferably from 10 to 30 xcexcm. Reduction of the impurity metal content is attained by heat-treating a starting carbon black at high temperature. The average particle size means an arithmetic mean value obtained by observing carbon black fillers dispersed on a circuit board at a magnification of xc3x9710,000 to xc3x97200,000 with an electron microscope and measuring a particle size of 100 fillers selected at random.
Impurity metals which become a problem because the amounts thereof are particularly large are, for example, alkali metals such as Na, K and Li; alkaline earth metals such as Ca, Mg and Ba; Fe, Cu, Cr, Ni, Al, and the like.
The clean graphitized carbon black filler of the present invention is added to a crosslinkable elastomer to give a crosslinkable elastomer composition. An adding amount of the filler is from 1 to 150 parts by weight (hereinafter referred to as xe2x80x9cpartxe2x80x9d), preferably from 1 to 60 parts on the basis of 100 parts of the elastomer component. If the filler is added more, an amount of the filler to be falling away increases, which causes generation of particles.
On the other hand, as the carbon black filler having an impurity metal content of not more than 100 ppm, there can be used a carbon black having a relatively large average particle size of as large as 500 to 700 xcexcm, for example, a high purity MT carbon black (Ultra-Pure N-990 available from Cancarb, Co., Ltd.) or a high purity carbon black obtained by cleaning a carbon black of usual grade (for example N-990 available from Cancarb, Co., Ltd., and the like). Though it is preferable that the impurity metal content is lower, preferred more is a content of not more than 30 ppm, more preferably not more than 10 ppm.
The above-mentioned clean carbon black filler of the present invention is added to a crosslinkable elastomer to give a crosslinkable elastomer composition. An adding amount of the filler is from 1 to 150 parts, preferably from 1 to 80 parts on the basis of 100 parts of the crosslinkable elastomer component. If the filler is added more, an amount of the filler to be falling away increases, which causes generation of particles.
The crosslinkable elastomer component is not limited particularly. When used as a starting material for a sealing member for semiconductor manufacturing equipment, a fluorine-containing elastomer or silicone elastomer is preferred.
Fluorine-containing elastomers which can be used preferably are those capable of being crosslinked with a peroxide crosslinking agent, or an imidazole, oxazole, thiazole or triazine crosslinking agent.
Examples of the fluorine-containing elastomer capable of being crosslinked with a peroxide crosslinking agent are as follows. Perfluoro elastomer comprising 40 to 90% by mole of tetrafluoroethylene, 10 to 60% by mole of perfluoro(vinyl ether) represented by the formula (1):
CF2=CFxe2x88x92ORf
wherein Rf is a perfluoroalkyl group having 1 to 5 carbon atoms or a perfluoroalkyl(poly)ether group having 3 to 12 carbon atoms and 1 to 3 oxygen atoms, and 0 to 5% by mole of a monomer giving a cure site. Vinylidene fluoride elastomer comprising 30 to 90% by mole of vinylidene fluoride, 15 to 40% by mole of hexafluoropropylene and 0 to 30% by mole of tetrafluoroethylene.
Thermoplastic perfluoro elastomer which is a fluorine-containing multi-segment polymer comprising an elastomeric fluorine-containing polymer chain segment and a non-elastomeric fluorine-containing polymer chain segment, in which the elastomeric fluorine-containing polymer chain segment comprises 40 to 90% by mole of tetrafluoroethylene, 10 to 60% by mole of perfluoro(vinyl ether) represented by the formula (1):
CF2=CFxe2x88x92ORf
wherein Rf is a perfluoroalkyl group having 1 to 5 carbon atoms or a perfluoroalkyl(poly)ether group having 3 to 12 carbon atoms and 1 to 3 oxygen atoms, and 0 to 5% by mole of a monomer giving a cure site, and the non-elastomeric fluorine-containing polymer chain segment comprises 85 to 100% by mole of tetrafluoroethylene and 0 to 15% by mole of a compound represented by the formula (2):
CF2=CFxe2x88x92Rf1
wherein Rf1 is CF3 or ORf2, in which Rf2 is a perfluoroalkyl group having 1 ito 5 carbon atoms.
Fluorine-containing multi-segment polymer comprising an elastomeric fluorine-containing polymer chain segment and a non-elastomeric fluorine-containing polymer chain segment, in which the elastomeric fluorine-containing polymer chain segment contains recurring units derived from 45 to 85% by mole of vinylidene fluoride and from at least one other monomer copolymerizable with vinylidene fluoride, respectively. Examples of the other monomer are hexafluoropropylene, tetrafluoroethylene, chlorotrifluoroethylene, trifluoroethylene, trifluoropropylene, tetrafluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, perfluoro(alkyl vinyl ether), vinyl fluoride, ethylene, propylene, alkylvinylether, and the like.
Cold resistant fluorine-containing elastomer prepared by radical polymerization in the presence of a di-iodine compound and comprising 0.005 to 1.5% by mole of iodine-containing fluorinated vinyl ether unit, 40 to 90% by mole of vinylidene fluoride unit and 3 to 35% by mole of perfluoro(methyl vinyl ether) unit (as case demand, hexafluoropropylene unit up to 25% by mole and/or tetrafluoroethylene unit up to 40% by mole may be contained) (JP-A-8-15753).
Copolymer of tetrafluoroethylene and propylene (U.S. Pat. No. 3,467,635), and the like.
As the peroxide to be used as a crosslinking agent in such peroxide crosslinking, those which have been used so far can be used. It is a matter of course that the peroxide which does not contain metal elements is preferred. Examples of the peroxide are 2,2-dimethyl-2,5-di(t-butylperoxy)hexane, and the like. As the crosslinking agent, for example, triallylisocyanurate may be used.
Fluorine-containing elastomers which are capable of being crosslinked with an imidazole, oxazole or thiazole crosslinking agent can provide an obtained molded article with very high heat resistance. Examples thereof are fluorine-containing elastomers containing a trafluoroethylene unit and the perfluoro(vinyl ether) unit represented by the above-mentioned formula (1) and having nitrile, carboxyl and/or alkoxycarbonyl as a crosslinkable group.
Examples of perfluoro(vinyl ether) are perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), perfluoro(propyl vinyl either) (PPVE), and the like. Among them, PMVE is preferred.
A proportion of the tetrafluoroethylene unit to the perfluoro(vinyl ether) unit is 40 to 90/60 to 10 in % by mole.
Examples of the crosslinkable group which gives reactivity for crosslinking to the fluorine-containing elastomer capable of being crosslinked with an imidazole, oxazole or thiazole crosslinking agent are nitrile, carboxyl and/or alkoxycarbonyl. Examples of alkoxycarbonyl are, for instance, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, and the like. A content of the crosslinkable group is not more than 5% by mole, preferably not more than 2% by mole.
Examples of the method to introduce such a crosslinkable group are a method of copolymerizing a monomer having a crosslinkable group or a group convertible to a crosslinkable group (copolymerizing method), a method of converting a polymerization initiating moiety of polymer end to carboxyl (end group converting method), and the like.
Examples of the monomer to be used for the copolymerizing method are a nitrile-containing monomer, carboxyl-containing monomer, alkoxycarbonyl-containing monomer, and the like represented by: 
wherein m is 0 to 5 and n is 1 to 8, 
wherein n is 1 to 4, 
wherein n is 2 to 5, 
wherein n is 1 to 6,
CF2=CF[OCF2CF(CF3)]nOCF2CF(CF3)X3
wherein n is 1 or 2, and 
wherein X3 is CN, COOH or COOR5, in which R5 is alkyl which may contain fluorine atom having 1 to 10 carbon atoms.
In case where at least one of end groups is carboxyl or alkoxycarbonyl, it is preferable to copolymerize a monomer having nitrile or, carboxyl from the viewpoint of crosslinking reactivity.
As a crosslinking agent to be used for the imidazole crosslinking, oxazole crosslinking or thiazole crosslinking, it is preferable to use a compound having at least two amino groups. Particularly from the viewpoint of enhancing heat resistance, preferred is a compound having at least two functional groups represented by the 
wherein R1 is any one of OH, NH2 or SH.
Examples of the compound represented by the formula (I) are those represented by the formula (II): 
wherein R1 is as defined above, R2 is xe2x80x94S2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, alkylene having 1 to 6 carbon atoms, perfluoroalkylene having 1 to 10 carbon atoms, a single bond or a group represented by the formula (III). 
Positions of NH2 and R1 to phenyl group may be the same or different in both functional groups (I) at the right and left sides.
Non-restricted examples of preferred alkylene of R2 which may be substituted are, for instance, non-substituted alkylene having 1 to 6 carbon atoms, perfluoroalkylene having 1 to 10 carbon atoms, and the like. Examples of perfluoroalkylene are: 
and the like. Those R2 are known as a bisdiaminophenyl compound in JP-B-2-59177 and JP-A-8-120146.
Though R2 may be bonded to any positions of the both right and left benzene rings, it is preferable that either of NH2 group or R1 is so bonded as to be at a para position from the viewpoint of easy synthesis and advancing a crosslinking reaction easily.
A Non-restricted examples of the crosslinking agent are, for instance, bisdiaminophenyl compound (for imidazole crosslinking) such as 2,2-bis-(3,4-diaminophenyl)hexafluoropropane, bis-(3,4-diaminophenyl)methane and bis-(3,4-diaminophenyl)ether; bisaminophenol compounds (for oxazole crosslinking) such as 2,2-bis-(3-amino-4-hydroxyphenyl)hexafluoropropane (generally called bis(aminophenol)AF); bisaminothiophenol compound (for thiazole crosslinking) such as 2,2-bis-(3-amino-4-mercaptophenyl)hexafluoropropane; and the like.
Those crosslinking agents give molded articles excellent in mechanical strength, heat resistance and chemical resistance, particularly having well-balanced heat resistance and chemical resistance.
Examples of the preferred silicone elastomer are, for instance, a silicone rubber, fluoro silicone rubber, and the like.
The elastomer composition can be crosslinked into products having desired forms. As a crosslinking method, though the above-mentioned peroxide crosslinking, imidazole crosslinking, oxazole crosslinking and thiazole crosslinking are preferable, other known crosslinking methods, for example, methods of triazine crosslinking, polyol crosslinking and polyamine crosslinking, methods of crosslinking by irradiating radioactive rays and electron beams, and the like may be employed.
An adding amount of the crosslinking agent is from 0.05 to 10 parts, preferably from 0.1 to 2.0 parts on the basis of 100 parts of the elastomer component and as case demands, the crosslinking accelerator is added in an amount of from 0.1 to 10 parts, preferably from 0.3 to 5.0 parts on the basis of 100 parts of the elastomer component. In addition, a processing aid, internal mold releasing agent, and the like may be added in an amount not lowering effect of the present invention.
The crosslinkable elastomer composition of the present invention can be suitably used for production of a molded article, particularly a molded article such as a sealing member for sealing of a semiconductor manufacturing equipment which is particularly required to be highly clean. Examples of the sealing member are O-ring, square ring, gasket, packing, oil seal, bearing seal, lip type seal, and the like.
In addition, the crosslinkable elastomer composition can be used for a variety of elastomer products, for example, diaphragm, tube, hose, various rubber rolls, and the like. Also the composition can be used as a coating material and a lining material.
The molded article of the present invention is suitable for a sealing member for sealing of a semiconductor manufacturing equipment which is used for a dry process such as a plasma etching equipment mentioned hereinafter and also a sealing member for sealing of a semiconductor manufacturing equipment, for example, a cleaning equipment to be used for a wet process since elution of metals can be reduced.
A molded article suitable for a dry process is one having an impurity metal content measured by an ashing analysis method of not more than 100 ppm and an increasing rate of particles generated by irradiating oxygen plasma of not more than 500%, preferably not more than 200%. Also an increasing rate of particles generated by irradiating CF4 plasma is not more than 700%, preferably not more than 500%. It is preferable that the number of particles increased by irradiating oxygen plasma is not more than 50xc3x97104/cm2.
It is preferable that a change in weight of the molded article after the irradiation of oxygen plasma is not more than 0.90% by weight, and a change in weight of the molded article after the irradiation of CF4 plasma is not more than 0.330% by weight.
A molded article suitable for a wet process is one having an impurity metal content measured by an ashing analysis method of not more than 100 ppm, preferably not more than 50 ppm. An amount of impurity metal extracted with H2SO4/H2O2 (4/1 in weight ratio) is not more than 100 ppb, preferably not more than 70 ppb, and an amount of impurity metal extracted with a 50% by weight aqueous solution of HF is not more than 500 ppb, preferably not more than 400 ppb.
In the present invention, the semiconductor manufacturing equipment is not limited particularly to equipment for manufacturing semiconductors and encompasses whole manufacturing equipment used widely in the field of semiconductors where a high degree of cleanliness is required, such as equipment for manufacturing a liquid crystal panel and plasma panel.
Examples of the semiconductor manufacturing equipment are as follows.
(1) Etching system
Dry etching equipment (for dry etching)
Plasma etching machine (for dry etching)
Reactive ion etching machine (for dry etching)
Reactive ion beam etching machine (for dry etching)
Sputter etching machine (for dry etching)
Ion beam etching machine (for dry etching)
Wet etching equipment (for wet etching)
Ashing equipment (for dry etching)
(2) Cleaning system
Dry etching cleaning equipment (for dry etching)
UV/O3 cleaning machine (for dry etching)
Ion beam cleaning machine (for dry etching)
Laser beam cleaning machine (for dry etching)
Plasma cleaning machine (for dry etching)
Gas etching cleaning machine (for dry etching)
Extractive cleaning equipment
Soxhlet extractive cleaning machine (for wet etching)
High temperature high pressure extractive cleaning machine (for wet etching)
Microwave extractive cleaning machine (for wet etching)
Supercritical extractive cleaning machine (for wet etching)
(3) Exposing system
Stepper (for wet etching)
Coater and developer (for wet etching)
(4) Polishing system
CMP equipment (for wet etching)
(5) Film forming system
CVD equipment (for dry etching)
Sputtering equipment (for dry etching)
(6) Diffusion and ion implantation system
Oxidation and diffusion equipment (for dry etching)
Ion implantation equipment (for dry etching)
(7) Cleaning system using hydrofluoric acid, hydrochloric acid, sulfuric acid, aqueous ozone, and the like (for wet process)
The present invention is then explained by means of examples, but is not limited to them.
Impurity metal contents of the carbon black fillers used in the following examples and comparative examples are measured by an ashing analysis method and are shown in Table 1.
(Content of Impurity Metals in Filler)
0.5 To 2.0 g of a carbon black filler is put in a clean platinum crucible, and heated at 600xc2x0 C. for two hours to carry out ashing sufficiently. To the ash left in the crucible is added 5 ml of hydrochloric acid, followed by dissolving by heating in a hot bath and then diluting with ultrapure water. Contents of metals of that solution are determined through atomic absorption analysis by using an atomic absorption photometer (Z8000 available from Hitachi, Ltd.). Metals to be detected are shown in Table 1. The contents of each metal in the filler are obtained by the following equation.       Metal content 
       (ppm)    =                    Concentration in
 solution  (ppm)                    Weight of filler  (g)              xc3x97          Weight of  solution  (g)      